I gave my son up for adoption? We reconnected recently?

I don’t know what to do about my son? We just recently reconnected I gave him up for adoption when he was 4 years old now he is 16. He visits me all the time and he brings his girlfriend who is much older then him she is 28 he told me they have been dating since he was 15 and they are getting married next year. I find this very wrong, I talked to his parents about this they just said it is his life and they love each other. My son just said She encourages my talents and gives me unconditional love and support and that she is the most important person in my life. I don’t know what to do? Isn’t this illegal?